mcp-rector-warm

Rector is great. Its cold start is not. Every rector process rebuilds its container before a single rule fires: 7 seconds per file on a real production codebase. Keep Rector warm, and every call after the first takes 0.68s. Same output as cold. ~10× faster.

Two ways in, one warm engine:

• an MCP server that gives your AI agent a fast Rector;
• a language server that puts Rector's fixes in your editor.

Who it's for • Get started • AI agent • Editor • Validation loop • Numbers • Docs

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Who it's for

You…	You get	Use
let an AI agent refactor PHP	Rector as a tool your agent calls after every edit	MCP server
want Rector in your editor	Rector's fixes flagged as you type, one click to apply	Language server
run Rector in a validation loop	A warm Rector you call file by file, without paying the boot each time	MCP server

Both ship in one package. Run one, or both side by side.

Same answers. Just faster.

• ~10× faster per call. 0.68s warm against 7.02s cold, at the median.
• Identical output. All 20 benchmark files gave the same answer warm and cold, and CI checks warm output against a fresh cold Rector run. Nothing to re-check.
• One-time boot. The first call costs about one cold run (~6.4s), once per session. An idle server costs nothing.
• Edit rector.php freely. Config changes apply on the next call. No restart.

Get started

composer global require dpt/mcp-rector-warm

That's the install. PHP 8.2+, Rector ^2.4 comes along as a normal Composer dependency. Now pick where Rector should run.

Rector in your AI agent

For: anyone who lets Claude, Copilot agent mode, Cursor, Cline or another agent refactor PHP.

• Your agent runs Rector after every edit, without waiting 7 seconds each time.
• Preview first. The agent sees the diff; files change only when it asks to write.
• Stays inside your project. Paths outside the working directory are refused.
• Any MCP client. Claude Desktop, VS Code, Cursor, Cline, Continue, Zed.

Add it to Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json on macOS, %APPDATA%\Claude\claude_desktop_config.json on Windows):

{
  "mcpServers": {
    "rector": {
      "command": "mcp-rector-warm",
      "args": [
        "--working-dir=/path/to/your/project",
        "--config=/path/to/your/project/rector.php"
      ]
    }
  }
}

Restart Claude and ask: "Run Rector on src/Foo.php". Done.

Full setup → VS Code and other clients, the rector_process tool, timeouts.

Rector in your editor

For: PHP developers who want Rector's suggestions where they write code, not in a terminal afterwards.

• Fixes appear as you type, on unsaved edits too, not only on save.
• One click to apply one rule, the whole file, or the whole project, without touching files that have unsaved changes.
• A broken file never looks clean. A syntax error or a bad config shows up as an error.
• Change rector.php, see it at once. Open files re-check when the config changes.

Point your editor's LSP client at:

rector-warm-lsp --working-dir=/path/to/project

for PHP files, with composer.json / rector.php as root markers.

Full setup → copy-paste configs for Neovim and Helix (tested in CI), Zed, Sublime Text and PhpStorm.

Rector in your validation loop

For: teams and tools that run Rector after every generated change, as a check.

• Start once, call per file. No boot on each check after the first.
• Plain MCP over stdio. Drive it from any MCP client library (Python, Node, Go…).
• Failures are real errors. A bad path, a missing config or a Rector exception comes back as an error, never as a silent pass.

mcp-rector-warm --working-dir=/path/to/project --config=/path/to/project/rector.php

Full setup →

The numbers

~10× faster per call. The first call boots Rector once, costing about the same as one cold run (6.4s). Every call after that takes 0.68s (median) instead of 7.0s cold.

Setup	median	p95
Cold rector process, every call	7.02s	9.00s
Warm, first call (one-time boot, once per session)	6.4s
Warm, every later call	0.68s	2.40s

20 files from a real production codebase: 144s cold, 30s warm including the one-time boot. All 20 warm answers matched the cold ones.

Method, caveats, reproduce it on your project →

Install

composer global require dpt/mcp-rector-warm

Puts mcp-rector-warm and rector-warm-lsp on your $PATH. As a project dependency, both are in vendor/bin/.

Documentation

• MCP server: every client setup, the rector_process tool, options, the call timeout, compatibility.
• Language server: editor setup, diagnostics, quick-fixes, unsaved buffers, fix-all, limits.
• How it works: architecture, config reloads, Windows and other PHP builds without pcntl.
• Benchmark: method, full numbers, how to reproduce.
• FAQ.
• The language server, for the Rector maintainers: design, correctness checks, known limits.

Credits

• Rector by Tomas Votruba and contributors — the engine doing all the real work. If you ship PHP, sponsor him.
• Model Context Protocol by Anthropic — the protocol that makes this kind of tool integration possible.
• mcp/sdk — official PHP SDK, used here for stdio transport + tool discovery.

Related

• Rector docs — config, rules, sets.
• Rector on Packagist — the upstream package.
• claude-supertool — DPT's batched-ops Claude Code companion; integrates this server as a validator.

License

Community License — see LICENSE. Built by Digital Process Tools.